Should I post it?

Bit of a tricky one. In one way i would say yes because you obviously do care and that will show but on the other hand what if she hasnt forgot about the friction between u, then it is a big no no.

It's not clear from your question what type of letter you wrote. If the letter is simply condolences on her loss, then by all means mail it. If nothing else, you'll be taking the high road, and can feel good about your behavior. It's a conventional enough action that she shouldn't take any offense. I agree with the previous answer, though about not expecting a reply or following up.

If it's to carry on the friction between you or anything else that might increase her burden at this difficult time, then don't send it.

What was the friction/ cause of the friction? Need to know before you send the letter. Some things take a long time to heal, and although you feel things have changed, she may not! Also, she is not likely to be thinking straight at the moment, so may take things the wrong way, depending on what your letter contains. She may look for reasons for her husbands death/someone to blame - a letter from you could give her someone to blame - particularly if her husband was the cause of the friction between you! In any case, my gut instinct without knowing any of the details is to leave it for a while.

If you lose someone by their own hand i:e Suicide, the grief that is felt can be twofold, you grieve for their loss & you grieve thro' blame (why did they do it).Its very difficult to put into words but hope you get my drift. Think very carefully before you send the letter especially as there seems to be some history between you. You may make matters worse!!.

Definitely. Right now she needs all the support she can get, and it might actually mean a lot to her that though the two of you had friction, something like this was something you never would have wished upon her and that your heart goes out to her. I am sure she will appreciate the sentiment.

Post it as long as the letter is nice and not hurtful. She needs lots of support at a time like this. This may even be something that can make her move on and you can be friends again.

Depending on what the letter says, you should. If you are telling her how you feel about her, you should make sure that an appropriate amount of time has passed.

No, it might come across a bit weird. Wait a bit and see if you can get on speaking terms first, at least 'Hello' in the street. Why do you feel the need to unburden yourself on her when she's grieving?

no..it's good that you wrote it though as it will help you to heal..leave her to deal with her problems or you may find this unbalanced person starts problems again..let her go on her life path and wish her well for your own sake. you could try writing a reply to yourself that you would like her to send to you and then a thank you/ resolution letter...burn them and then move on

If post means mail, then yes. She may appreciate the thought.